Horse Summer Sores and Habronemiasis

Summer sores are intensely itchy, non-healing skin lesions in horses caused by aberrant fly larvae, requiring specific treatment and fly control.

Key Facts

Summer sores (cutaneous habronemiasis) result from Habronema fly larvae deposited in wounds or moist skin areas
The larvae cause an intense immune reaction creating raised, ulcerated, caseous (cheesy) lesions
Lesions typically occur on wounds, the sheath, medial canthus of the eye, and moist skin areas
Flies deposit larvae on existing wounds or mucous membranes during feeding in warm months
Treatment involves ivermectin to kill larvae, corticosteroids to reduce inflammation, and fly control
Lesions heal slowly and may require multiple treatment cycles; surgical removal is sometimes needed

Welfare Considerations

Summer sores cause intense, persistent itching that horses cannot relieve through normal scratching behaviors. The characteristic caseous granuloma tissue resists normal wound healing, meaning affected horses carry chronically irritated, itchy lesions throughout the fly season that worsen each time flies deposit further larvae. The eye and sheath locations cause particular distress - ocular lesions impair vision and cause blepharospasm, while sheath lesions cause discomfort during urination and movement. Prompt treatment with ivermectin at the first sign of summer sores, combined with aggressive fly control during warm months, significantly reduces the duration and severity of welfare harm from this condition.

What You Can Do

Treat wounds promptly and keep them covered to prevent fly access during warm months
Apply fly repellent to wounds and moist skin areas, particularly around the face and sheath
Use fly masks to protect eye corners and muzzle areas from fly larval deposition
Start ivermectin treatment promptly when summer sores are suspected - do not wait for them to grow
Combine ivermectin with corticosteroids under veterinary guidance to reduce inflammation
Implement comprehensive fly control including manure management and insecticide use on the premises